ABSTRACT Three Dimensional Engineered Structures from Graphene Oxide Atomic Layers by Soumya Vinod Two dimensional atomic layered materials have gained much attention due to the fascinating physical phenomenon seen in them. However to be utilized for direct applications, there is a need to build three dimensional structures that can combine the intrinsic properties of the 2D material with the novel behavior that originates from assembly of the macroscopic architecture. Graphene has been the most studied 2D material owing to its unique structure and properties. Graphene Oxide (GO) which is graphene with oxygenated species has emerged in prominence due to the exciting properties it has to offer from combination of layered structure and functionalities present. GO is a major precursor utilized in creating various carbonaceous materials. In this work, GO is used as the fundamental unit in building foam, paper and composite with detailed analysis of their formation and properties. Chapter 1 discusses the emergence of 2D materials, the popularity of graphene based materials and their use as building blocks for creating 3D structures. The advantage of GO to be used as precursor in developing 3D materials are reviewed. In Chapter 2, unique structural formation of a foam from the interaction of GO and hexagonal boron nitride (h-BN) is investigated. Electron microscope imaging and mechanical characterization provide insights into the formation and the mechanical response of the foam. The novel orderly stacked layered architecture demonstrates enhanced mechanical strength and structural stability. In Chapter 2, free standing GO film is synthesized and the mechanical behavior based on sliding of layers is studied. A strain rate dependent plasticity where the GO film behavior transitions from brittle to ductile with decrease in strain rate is observed. Chapter 3 explores GO as a substitute for epoxies towards synthesizing thermally conducting epoxies. The interactions of the epoxy functional groups in GO with polymercaptan based hardener forms a resin that provides high thermal stability and adhesion between surfaces. This elevates GO as the main constituent in the epoxy system and eliminates its limitation as a filler material. Chapter 5 summarizes the findings and reviews challenges associated with building controlled macroscopic architecture from 2D fundamental units followed by future advancement directions. Acknowledgments I express my sincere gratitude to my advisor, Prof. Pulickel Ajayan for providing me the opportunity to work in his research group and for all his encouragement, patience and motivation during the course of the study. This thesis would not have been possible without his guidance, support and advices. I thank our lab manager and Faculty fellow, Dr. Robert Vajtai for providing directions in research and the valuable discussions. I would like to thank Prof. Jun Lou and Prof. Yildiz Bayazitoglu for serving on my committee. Their constructive comments and valuable suggestions have helped me immensely in the successful completion of my thesis. I sincerely appreciate the support by my present and former lab members Dr. Chandra Sekhar Tiwary, Dr. T.N. Narayanan, Dr. Jaime Taha, Dr. P.M. Sudeep, Sehmus Ozden, Alin Cristian Chipara, Kaushik Kalaga, Preston Shaw, Juny Cho and collaborators Prof. Douglas S. Galvao, Dr. George John, Dr. Pedro Alves da Silva Autreto, Dr. Leonardo Machado and Dr. Vipin Agarwal. I would also like to thank SEA research scientists Dr. Gang Liang, Dr. Wenhua Guo and Dr. Bo Chen who have been very supportive in material characterization. I thank the support from MSNE and previous MEMS staff Jessica McVey, Kim Hardy, Linda Lerma, Cindy Wilkes, Leah Benard-Boggs and Sherry Vanderslice. Thanks to Maria for all her love and working so hard to make life of students at Rice easier. It was a pleasure to work with all the members of Ajayan research group and their insightful comments and suggestions have benefited a lot in the course of my research. I am really thankful to my advisor’s lovely family; his wife Poornima and daughters Anakha and Ahi for v their friendship, care and support. Special thanks to my parents, my brother Ranjith and my in-laws for their unconditional love and constant encouragement. I cannot express how thankful I am to my husband Vinod and our sons Aadit and Ayan for being there with me for everything and providing me the comfort that has made my PhD an enjoyable experience. Contents Acknowledgments..................................................................................................... iv Contents ................................................................................................................... vi List of Figures ............................................................................................................ ix Nomenclature .........................................................................................................xvii Chapter 1 Introduction............................................................................................................... 1 1.1. Two Dimensional Materials...................................................................................... 2 1.2. Graphene and its derivatives ................................................................................... 4 1.3. Graphene Oxide........................................................................................................ 8 1.3.1. GO synthesis methods....................................................................................... 9 1.3.2. Structural models ............................................................................................ 11 1.3.3. Properties ........................................................................................................ 14 1.4. Graphene based engineered structures ................................................................ 18 1.4.1. Template assisted method .............................................................................. 19 1.4.2. Solution based self-assembly .......................................................................... 21 1.5. Graphene Oxide as building units for 3D materials ............................................... 23 1.6. Experimental Methods........................................................................................... 25 1.6.1. GO synthesis using improved Hummer’s method........................................... 25 1.6.2. Structural Characterization.............................................................................. 26 Chapter 2 Graphene Oxide Foam Reinforced with Hexagonal Boron Nitride.............................. 38 2.1. Synthesis and Material Characterization ............................................................... 40 2.1.1. GO-BN Foam synthesis .................................................................................... 40 2.1.2. Scanning and Transmission Electron Microscopy ........................................... 44 vii 2.1.3. Spectroscopy and X-ray diffraction ................................................................. 49 2.2. Mechanical Characterization.................................................................................. 50 2.3. Molecular Dynamics Simulation............................................................................. 55 2.4. Reduction of the foam ........................................................................................... 61 2.4.1. Reduction experiment ..................................................................................... 62 2.4.2. Morphology analysis........................................................................................ 65 2.4.3. Mechanical Characterization ........................................................................... 68 2.5. Discussion............................................................................................................... 71 Chapter 3 Graphene Oxide Free Standing Films ........................................................................ 74 3.1. Synthesis and materials characterization .............................................................. 75 3.1.1. GO film synthesis ............................................................................................. 75 3.1.2. Scanning and transmission electron microscopy ............................................ 76 3.1.3. Spectroscopy.................................................................................................... 78 3.2. Mechanical Test...................................................................................................... 80 3.2.1. Tensile Test ...................................................................................................... 80 3.2.2. Bending test..................................................................................................... 82 3.3. Molecular Dynamics Simulation............................................................................. 84 3.4. Stability of GO films................................................................................................ 87 3.5. Applications............................................................................................................ 89 3.6. Discussion............................................................................................................... 91 Chapter 4 Graphene Oxide Epoxy ............................................................................................